Re: [SystemSafety] SIL ratings to be scrapped?

From: SPRIGGS, John J < >
Date: Fri, 23 Aug 2013 09:56:04 +0000

The SILs of the Defence Standard were different from those of IEC61508, which fact I have seen cause problems on more than one project... I would not be at all surprised if the chattering classes take a DEF.STAN. change made almost a decade ago as an indicator of an imminent change in 61508. From: systemsafety-bounces_at_xxxxxx Sent: 23 August 2013 10:41
To: Bielefield SafetyList
Subject: Re: [SystemSafety] SIL ratings to be scrapped?

It is possible that this rumour might relate to the current work underway to revise Def Stan 00-55, Requirements for Safety Related Software in Defence Systems.

A system of SILs was defined Def Stan 00-56 Issue 2, Safety Management Requirements for Defence Systems (1996), which was also used in Def Stan 00-55. However, SILs were removed from the mandatory part of 00-56 in Issue 3 (2004) as part of the move to a goal-based approach to requirements setting. Instead, the guidance in 00-56 Part 2 discussed setting integrity requirements in generic terms, rather than using a specific SIL scheme. However, the guidance made it clear (in Annex C, section C.2) that SIL schemes could still be used where they were suitable.

Def Stan 00-55 was made obsolescent by the release of 00-56 Issue 3, and has not been re-issued. However, new work is currently underway to revise both standards. I have not seen recent drafts, but it is likely that neither standard will define a system of SILs, or require use of a specific SIL scheme. That said, it is also likely that use of suitable standard that incorporates SILs or a similar concept could still be part of the argument to demonstrate compliance with either 00-55 or 00-56.


          James Inge

Sent: 21 August 2013 16:59
To: safetyyork_at_xxxxxx Subject: Re: [SystemSafety] SIL ratings to be scrapped?

I think there may have been a misunderstanding somewhere along the way here.

UK MoD implemented the use of SILs into many of their projects a few years ago and these are now being replaced by SIRs - Safety Integrity Requirements ( High / Medium / Low) . . . Don't know if this is a pointer in any direction . . .

        Many Thanks
        Alan G. Dominey
        Electrical Safety Engineer
        Torpedo Capability Contract Project Surveillance Manager
        Spearfish Safety Group

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Sent: 21 August 2013 15:26
To: 'Bielefield Safety List'
Subject: [SystemSafety] SIL ratings to be scrapped?

Hi all,

I have just been taking to one of my customers who do control systems for industrial systems. They have been told by someone they are doing a system for that SIL ratings will "soon be scrapped". Apparently "It will be replaced by ALARP". This seems like a completely misunderstood half a message. Though usually on this sort of thing there is a grain of reality (if miss reported or miss represented) in there somewhere.

I know I have not been paying attention over the summer but I haven't seen anything. Is there a move on any standard to change from SIL ratings for projects?



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systemsafety_at_xxxxxx Received on Fri Aug 23 2013 - 11:56:22 CEST

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